This invention relates to a variable area diffuser, and more particularly, the invention relates to geometry of the diffuser vanes.
Variable area diffusers use multiple vanes that are rotated between different angular positions to vary the throat size of the diffuser. Variable area diffusers can be used in conjunction with, for example, superchargers to vary the flow through an air conditioning system of an aircraft. The vanes are supported between a backing plate and a shroud of the diffuser. A small clearance a few of thousandths of an inch is provided between the vane and backing plate and shroud to minimize the loads and wear between these components. As a result, the life of the diffuser vanes is improved.
Under some supercharger operating conditions it is possible to produce an unstable airflow condition. The unstable airflow condition creates a hydrodynamic bearing-like layer between the vanes and the backing plate and shroud. As a result, the vanes are permitted to float freely between the backing plate and shroud. As the length of the vanes increases, the vanes may have a resonant frequency within the operating range of the supercharger. As a result, in some applications the vanes may reach resonant frequency and fail as the vanes oscillate violently at a high frequency between the backing plate and shroud.
What is needed is a diffuser vane geometry that is not excited at its resonant frequency during normal supercharger operating conditions.